LM4780 problem

[Lamicz]

Hi! I posted photo of my new LM4780 amp, its sounding very good, but I hear in speakers when a light switch in my flat is turned on or off - when somewhere an electric arc is started... I dont know how filter it out... Thx for any help

[Peter Daniel]

Some people recommended installing input shunt capacitor: 300pF or similar.

You might also try to improve grounds in your system.

[lazyfly]

Used Cc across the pins (220pF from memory) on a 3886 to kill off the blip from aquarium fluoro lights that worked well. A stereo setup would have one across pins:
-IN A
+IN A

another across:
+IN B
-IN B

I think... best wait for verification.

Details on page's 1, 7 & 8 in the datasheet.

[youyoung21147]

try to shield and ground your case properly, with iron plates for example. The cap across the input pins is a simpler solution and works too.

[jackinnj]

the bypass capacitors on the V+ and V- pins (100nF ceramic + 10uF) will help a lot. Also -- you can use ferrite beads on the input lines -- most likely you are picking up a transient on the power supply lines --

you can also box up the LM4780 (but not the heatsink) in a box made of Printed circuit material -- just solder up the sides.

[youyoung21147]

Originally posted by jackinnj
the bypass capacitors on the V+ and V- pins (100nF ceramic + 10uF) will help a lot. Also -- you can use ferrite beads on the input lines -- most likely you are picking up a transient on the power supply lines --

you can also box up the LM4780 (but not the heatsink) in a box made of Printed circuit material -- just solder up the sides.

Why not the heatsink ? I assume it must also be grounded if you want to "enclose" the chip in a shielded area. Or do you mean keeping it out, grounded properly, to avoid heat issues ?

[jackinnj]

Originally posted by youyoung21147



Why not the heatsink ? I assume it must also be grounded if you want to "enclose" the chip in a shielded area. Or do you mean keeping it out, grounded properly, to avoid heat issues ?

the heatsink must be exposed to air movement (i.e. you can use a fan to move air to remove the heat) but you can enclose the entire LM4780 and PCB within a chasis.